The present invention relates to the manufacture of wire in general, and more particularly to improvements in a method and apparatus for forming and treating metallic rods, preferably steel rods, prior to drawing through a wire die.
It is known to treat a steel rod which issues from the last pass of a rod mill, and whose temperature is in the range of approximately 1000.degree. C., with a view to effect desirable structural changes in the material of the rod before the latter is introduced into a wire die. The treatment may involve abruptly cooling the rod immediately behind the last pass of the rod mill so that the temperature of the rod drops below the Ac.sub.3 point. The cooling may be carried out by causing the rod to exchange heat with water and/or air, fluidized heat carriers or molten suspensions or solutions of salts or the like. One of the presently known heat exchanging agents is sodium nitrate.
A drawback of presently known methods and apparatus (including those using sodium nitrate) for treating steel rods prior to drawing in a wire die or the like is that they cannot be used on a large scale for mass-production of steel wire. The main reason is believed to be that it was not possible to maintain the temperature of the cooling or heat exchanging medium within a sufficiently narrow range to insure uniform withdrawal of heat from each and every increment of the rod. Such uniform withdrawal of heat is necessary in order to insure that each portion of the rod undergoes an optimum structural change prior to introduction into the wire die. The difficulties in connection with the establishment and maintenance of an optimum temperature range for the coolant are attributed to the fact that the speed of the rod which issues from the mill is likely to vary, that the rod introduces into the coolant very large amounts of heat energy, and that the maintenance of a predetermined temperature range may involve cooling and/or heating the coolant as well as insuring that each and every zone or portion of the coolant is maintained at the same temperature. Additional problems arise during starting of conventional apparatus because the heating of coolant to a desirable optimum temperature to effect satisfactory structural changes in the material of the rod takes up too much time. As a rule, the rod which issues from the mill is spread out fanwise by the transporting means or is converted into a bundle of abutting coils prior to introduction into the cooling medium. The coiling or winding of the rod takes place in a vessel which contains the cooling medium, or the bundle is formed prior to introduction into the vessel. In each instance (i.e., during spreading or during coiling), neighboring portions of the rod contact each other so that they are not cooled to the same extent as those portions which are in direct contact with the coolant. The result is a non-uniform treatment, i.e., structural changes in those portions of the rod which are in direct contact with each other are often basically different from those taking place in rod portions which are in direct contact with the coolant, such as molten sodium nitrate. This affects the quality of the ultimate product and presents problems during drawing through the die.